Liquefied petroleum gas (LPG) may be directly injected to engine cylinders. The liquefied petroleum gas may be supplied to a direct fuel injector in a liquid state, and the liquid may vaporize within the cylinder after it is injected into the cylinder to cool cylinder contents and support combustion within the cylinder. By cooling cylinder contents, the engine may be less prone to engine knock so that the engine may be operated with a higher compression ratio to improve engine efficiency. Thus, engine operation may benefit from operating an engine with LPG; however, the LPG may change state to a gas in the fuel system if its pressure is too low or if it becomes supercritical. In a supercritical state, it may be much more difficult to determine the amount of fuel being injected to the engine. Additionally, more energy may be consumed to inject the fuel to the engine because fuel pumps may be less efficient pumping fuel in a supercritical state. Consequently, the benefits of supplying LPG to the engine may be lost or reduced.
One approach that at least partially overcomes the above issues and achieves the technical result of ensuring liquid fuel is supplied to a direct injection fuel pump is disclosed herein. In particular, the approach provides for a method, comprising: increasing cooling of fuel supplied to a direct injection fuel pump in response to direct injection fuel pump volumetric efficiency being less than a threshold.
By increasing cooling of fuel supplied to a direct injection fuel pump in response to direct injection fuel pump volumetric efficiency, it may be possible to maintain flow of liquid fuel to the direct injection fuel pump so that the possibility of engine fueling errors may be reduced. In particular, fuel supplied to the direct injection fuel pump may be cooled so that the fuel does not reach a supercritical state where its mass may be difficult to determine. Additionally, in some examples, pressure of fuel supplied to the direct injection fuel pump may be increased so that the fuel does not reach a supercritical state.
The systems and method disclosed may provide several advantages. For example, the approach may provide improve engine air-fuel ratio control. Additionally, the approach may provide for supplying fuel to an engine using less energy. Further, the approach may reduce degradation of fuel system components.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.